星载柔性可展桁架结构的模态试验与分析
Modal Test and Analysis of Flexible Deployable Truss Structure

对于基频小于2Hz的小卫星柔性可展结构，因为普通的锤击测试法只能激发出柔性结构的局部模态，很难激发出整体模态。针对文中描述的小卫星柔性可展桁架结构，提出一种新颖的模态测试方法：采用绳索-柔性弹簧的重力卸载系统消除重力对模态的影响。利用绳索在19个花盘处同时进行重力卸载，并在吊索中部安装柔性弹簧避免对花盘产生附加刚度;将柔性可展结构分别置于水平、竖直两个方向进行模态试验，采用超低频激振系统进行激励，并利用激光位移传感器采集试验数据，提高了试验结果的准确性。试验结果表明：竖直悬吊方式更为准确，并将试验数据与有限元分析结果对比分析，结果显示两者较为接近，从而验证了试验方法的准确性。
The first natural frequency of flexible deployable structures is mostly less than 2Hz. Low mode has caused difficulties to modal testing of such structures, because the average hammering test method can only stimulate the local modes rather than global mode of flexible structure. For flexible deployable truss structure described in this paper, a novel modal test method is proposed. The rope-spring gravity unloading system is used to eliminate the effect of gravity on modal. The ropes are set at 19 faceplates to unload the gravity at the same time. The flexible spring in the rope is used to release additional stiffness. When tested, flexible deployable structures are placed in horizontal and vertical directions in high-precision. The ultra-low frequency vibration exciter is the source of vibration. And laser displacement sensor is used for data collection. Both of them can increase the accuracy of the test results. Finally, the test results show that the vertical suspension method is more accurate. In addition, the test results are contrasted with that of finite element analysis, and it can be found out that two of them are approximately the same to verify the validity of the trial design.